The present invention relates generally to improvements in flotation type particle separating systems and more particularly to such improvements in flotation systems employing air bubbles rising through a flotation compartment to carry certain particle types to the top of that compartment while other particle types settle to the bottom of the compartment and to such systems which employ water conservation techniques.
A wide variety of refining, separating and concentration enhancing techniques employing air or water flotation separation or combinations thereof are know. Typical of such systems and exemplary of environments in which the present invention finds particular utility are U.S. Pat. Nos. 3,371,779; 4,287,054; and 4,394,258 as well as the patents cited therein.
Commercially valuable minerals, for example, metal sulfides, apatitic phosphates and the like, are commonly found in nature mixed with relatively large quantities of gangue materials, and as a consequence it is usually necessary to beneficiate the ores in order to concentrate the mineral content thereof. Mixtures of finely divided mineral particles and finely divided gangue particles can be separated and a mineral concentrate obtained therefrom by well know froth flotation techniques. Broadly speaking, froth flotation involves conditioning an aqueous slurry or pulp of the mixture of mineral and gangue particles with one or more flotation reagents which will promote flotation of either the mineral or the gangue constituents of the pulp where the pulp is aerated. The conditioned pulp is aerated by introducing into the pulp a plurality of minute air bubbles which tend to become attached either to the mineral particles or to the gangue particles of the pulp, thereby causing these particles to rise to the surface of the body of pulp and form thereat a float fraction which overflows or is withdrawn from the flotation apparatus.
Typical of such flotation apparatus for accomplishing the foregoing is that disclosed in U.S. Pat. No. 3,371,779. In such apparatus, the conditioned pulp is introduced into a flotation compartment containing a relatively quiescent body of an aquesous pulp, and aerated water is introduced into the lower portion of the flotation compartment through orifices formed in the bottom wall of the flotation compartment. A body of aerated water is established in a hydraulic or aeration compartment disposed directly below the flotation compartment by introducing air and water into the hydraulic compartment while simultaneously dispersing a multitude of fine air bubbles throughout the water in the hydraulic compartment. The body of aerated water in the hydraulic compartment is in fluid communication with the aqueous pulp in the lower portion of the flotation compartment through the aforementioned orifices formed in the bottom wall of the flotation compartment. An overflow fraction containing floated particles of the pulp is withdrawn from the top of the body of aqueous pulp and an underflow or nonfloat fraction containing nonfloated particles of the pulp is withdrawn from the pulp in the lower portion of the flotation compartment.
In the aforementioned U.S. Pat. No. 4,287,054, aerated water is introduced into the hydraulic compartment by employing a plurality of aspirator assemblies and a more uniform distribution of air bubbles entering the flotation compartment is achieved by employing a plurality of downwardly extending annular baffle plates of uniform depth beneath the constriction plate which forms the separation between the hydraulic compartment and the flotation compartment so that radial migration of the air bubbles along the lower surface of that constriction plate is minimized.
In the aforementioned U.S. Pat. No. 4,394,258 a water conservation or recirculating scheme is employed and the concept of sealing water introduced beneath the apertured constriction plate so that the upward velocity of water passing through the apertures in the constriction plate is greater than the settling rate of particles descending to the bottom of the flotation chamber thus preventing passage of those particles through the apertures in the plate is disclosed.
The structure set forth in these prior art patents have met with considerable commercial success and provide quite adequate results in certain particle separating processes, however, in other applications, for example, the separation or concentration of certain copper ores, these prior art processes are deficient in one or more respects.
In the copper ore refining exemplary application, the raw material is extracted from relatively deep mine shafts and frequently those shafts employ timbers for shoring up the walls and ceilings of the shafts. Frequently, small pieces of wood from the mine shaft shoring shows up in the ore to be refined and it has been found that these small wood particles are not adequately separated by the flotation process but rather accumulate and clog up the water recirculating system, for example, of the type disclosed in the aforementioned U.S. Pat. No. 4,394,258. Accordingly, an economical and expeditious scheme for eliminating such wood particles or other foreign matter which is not adequately separated out by the flotation process from the water recirculating apparatus would be highly desirable.
While the system of annular baffles beneath the constriction plate as disclosed in the aforementioned U.S. Pat. No. 4,287,054, provides adequate uniformity of the rising air bubbles in the upper or flotation chamber for many flotation separation purposes, a greater uniformity or control over the dispersion of bubbles in the flotation compartment is required in some applications.
The arrangement for introducing aerated water into the system of the U.S. Pat. No. 4,287,054, and a similar system originally attempted in the present invention, include a number of radially inwardly extending pipes beneath the constriction plate, each having its own aspirator. With these arrangements, when a particular aspirator becomes clogged, the associated pipe no longer supplies aerated water and, thus, the flow of bubbles upwardly, within the flotation chamber, becomes nonuniform and erratic particle separation occurs. These erratic results, as well as the tendency of the individual small aspirators to become clogged and nonfunctioning, are obviated in the present invention.
The configuration of the constriction plate and the manner in which seal water is introduced into the system of the aforementioned U.S. Pat. No. 4,394,258 may in some applications not provide adequately uniform air bubble distribution within the flotation compartment or may fail to provide sufficiently uniform seal water flow through the constriction plate. It has also been found in this system that a more gently sloping constriction plate both minimizes the premature withdrawal of sediment from the flotation compartment and enhances the uniformity of seal water flow and bubble dispersion through the flotation compartment.
Devices of the type described frequently introduce air into the system using aspirators where water flow through a venturi or nozzle of diminished cross-sectional area creates a suction pulling outside air into the water flow. Particularly when the water flow is recirculated, particulate contamination may lodge in and block flow through the aspirator, requiring a nonproductive and often quite costly shutdown of the system until the blockage is cleared.
Also, devices of the type described may experience the problem of so-called short-circuiting in some applications. The phenomenon of short-circuiting occurs when there is a downward material movement along a generally conical path within the separation chamber which is too rapid and, therefore, includes an unacceptably high concentration of the component or particles types, which should migrate upwardly within the system and be separated as a froth overflow at the top of the separator.